1. Field of the Invention
This invention relates generally to a battery bypass assembly and, more particularly, it relates to a battery bypass assembly for a spacecraft battery supply system which removes a failing battery cell from the battery supply system without causing power loss within the battery supply system.
2. Description of the Prior Art
Today, spacecraft in high-earth orbit, such as satellites and the like, are becoming more and more important in supplying technological advances to feed an increasing government, business, and consumer appetite. In order to provide an uninterrupted power supply to the spacecraft, the spacecraft has a battery supply system. The conventional spacecraft battery supply system is typically constructed from a plurality of battery cells arranged in series or parallel arrays, according to the required voltage and current output of the battery supply system. While most of the equipment within the spacecraft can properly operate at voltages of twenty-two (22 V) volts, twenty-four (24 V) volts, or twenty-six (26 V) volts, the desired total voltage to power the spacecraft is twenty-eight (28 V) volts in the event that one or more of the battery cells becomes inoperable.
In most spacecraft, the plurality of battery cells are either nickel cadmium (NiCd), nickel-metal hydride (NiMH) batteries having an approximate voltage of between 1.2 volts and 1.5 volts or lithium ion battery cells having an approximate voltage of between 2.0 volts and 2.5 volts. While nickel-metal hydride batteries are typically used in spacecraft today, lithium ion batteries are rapidly becoming the power source of choice for future space applications. The lithium ion batteries exhibit high energy and power both per unit volume and per unit weight in comparison with other rechargeable type batteries.
The design of the battery supply system of a spacecraft presents special challenges not typically found in sub-orbit applications. The spacecraft battery supply system must continue to operate in an acceptable manner for years while physically inaccessible to maintenance and repair because the spacecraft is in high-earth orbit. When one of the battery cells starts going bad or otherwise loses power, the failing or failed battery cell ceases pumping voltage. As the battery cell continues to decline, the battery cell actually becomes a resistor to the entire battery supply system pulling power from the battery supply system and creating excessive heat. Loss of power and excessive heat can interfere with the operation of the spacecraft and could, potentially, cause the battery cell to explode.
In the past, a battery bypass has been used for each battery cell to bypass any battery cell which loses power to remove the battery cell from the battery supply system. Otherwise, as mentioned above, if one of the battery cells were to fail to an open circuit condition, the battery would be rendered inoperable in the open-circuit state. The battery bypass permits the failed battery cell to be bypassed, so that the battery supply system continues to functions although at a slightly diminished performance level. Therefore, it is common practice to overdesign the spacecraft battery supply systems according to the statistical probabilities of failure of one or more of the battery cells in the battery supply system, so that, through the use of the battery bypass, the battery supply system can continue to function in an acceptable manner.
Previous battery cell management devices for the battery supply system typically used diodes or a relay device to short out failed cells. Unfortunately, these conventional battery bypass systems were unreliable, heavy, and generated excessive heat which could damage the entire spacecraft and its functions. Furthermore, conventional battery bypass systems can suffer damage during launch thereby jeopardizing the entire functionality of the spacecraft upon battery supply system failure.
Accordingly, there exists a need for a battery bypass assembly which can remove individual battery cells from the battery supply system. Additionally, a need exists for a battery bypass assembly which is lightweight and reliable for high-earth orbit applications. Furthermore, there exists a need for a battery bypass assembly which safely maintains a battery supply system in an operating condition with all types of rechargeable battery cells.
The present invention is a battery bypass assembly for bypassing a first battery cell electrically connected to a second battery cell. Each battery cell has a first battery contact and a second battery contact. The battery bypass assembly comprises a housing having a first bypass contact and a second bypass contact. Voltage sensing means is mounted within the housing and is electrically connected between the first battery contact and the second battery contact for sensing a predetermined voltage loss in the battery cell. An expansive material within the housing expands upon the voltage sensing means sensing a predetermined voltage loss in the battery cell. A plunger mechanism is slidably mounted within the housing and is moveable from a first position to a second position. Maintaining means maintains the plunger mechanism in the first position and is moveable to allow the plunger mechanism to move into the second position. Actuating means contacts the expansive material and the maintaining means for moving the maintaining means upon expansion of the expansive material wherein the plunger mechanism, upon reaching the second position, bypasses the first battery cell. The present invention additionally includes a battery bypass mechanism for bypassing a battery cell. The battery cell has a first battery contact and a second battery contact. The battery bypass mechanism comprises a first bypass contact electrically connected to the first battery contact and a second bypass contact electrically connected to the second battery contact. Contact means are selectively movable to close the circuit between the first battery bypass contact and the second battery contact. Expansive actuating means actuate movement of the contact means to close the circuit and bypass the battery cell upon occurrence of a predetermined event.
The present invention further includes a method for bypassing a battery cell with a battery bypass assembly. The battery bypass assembly has a first bypass contact electrically connected to a first battery contact and a second bypass contact electrically connected to the second battery contact. The method comprises selectively moving a conductive bar between the first battery bypass contact and the second battery contact from a first position to a second position to close the circuit, providing a plunger rod within an expansive material, expanding the expansive material upon the occurrence of a predetermined event, substantially ejecting the plunger rod from the paraffin material, moving the conductive bar to the second position, and closing the circuit and bypassing the battery cell.